The present invention relates to optical fibers, and in particular to a packaging and assembly platform capable of accurately and easily connecting one or more optical fibers to one or more optical components having functions, such as optical detection, optical signal branching, optical multiplexing, optical switching, optical modulation and/or optical transmission. The present invention also describes optical modules comprising one or more optical components and such one or more packaging and assembly platforms.
As disclosed in U.S. Pat. No. 6,222,967, xe2x80x9cPackaging Platform, optical modules using the platform, and methods for producing the platform and the module,xe2x80x9d an optical component using a planar optical waveguide circuit, connection between an optical waveguide and an optical fiber requires alignment precision of the order of microns. Simplifying this connection is very important in reducing the manufacturing cost. An optical component which processes fast signals also involves fine electrical wiring, and thus requires a fan-out structure for electrical connection. An optical device generally needs sealing to achieve reliability. In an optical module having structures for a fiber pigtail and electrical wiring, it is necessary to seal large capacity regions above these structures. This has caused problems relating to packaging capacity and sealing effect.
Moreover, optical modules may have to implement many different types of components which can include lenses, individual gratings, thin film filters, isolators and/or other components which would need to be aligned and secured.
It is disclosed in the aforementioned patent that an improvement in the prior art of packaging and assembling optical components can be made by forming a packaging platform containing patterns which could be used to align optical waveguide components. It is further disclosed that this packaging platform could be made by injection molding or transfer molding. One class of materials discussed which could be used to create the packaging platform is synthetic resins. One specific class of synthetic resin discussed consisted of a thermosetting resin which contained inorganic fillers such as Talc, Mica, Calcium Carbonate, clay, alumina, alumina silicate, silica, zinc oxide, carbon, aluminum hydroxide, asbestos fiber, glass fiber and carbon fiber.
The aforementioned patent also mentions the use of ceramic as a packaging platform material, but no specific ceramic material is disclosed and no process for producing a module using ceramic was disclosed. Ceramic materials such as Alumina are mentioned, but only as an inorganic filler to a synthetic resin. In fact, the term ceramic is an extremely broad term used to include structural clay products, whitewares (dishes), refractories, glasses, abrasives and even cements. Most of these materials are not suitable for mounting and/or packaging optical, optoelectronic and/or electronic components. One type of ceramic material is fabricated using one or more powders, which are wet or dry pressed into a desired shape using either a hot or cold die. These materials are not discussed in the aforementioned patent.
Moreover, in embodiment 17 in the aforementioned patent, where the use of ceramic as a packaging platform is disclosed, the problem of shrinkage of the ceramic during firing or sintering is mentioned, which caused a deformation in the substrate. This deformation prevented the precise alignment of optical fibers or waveguides or other optical components. In order to resolve this, features were made by precision dicing into the ceramic substrate after firing or sintering, which were used for alignment in the transverse direction.
Thus features formed by injection or transfer molding of ceramic materials for the use of aligning optical fibers or waveguides or optical components were not disclosed in the aforementioned patent.
In addition, many aspects of sintered ceramic substrate formation were not discussed in the patent which would further inhibit the accurate formation of features in ceramic substrates after sintering. One such aspect includes so called xe2x80x98grain growthxe2x80x99 during sintering. In the case of Alumina ceramic substrates, this grain growth is essentially the assembly of A12O3 crystal-like structures which can extend outward from the surface of the molded pre-fired material. These grains can be greater than 1 micron in size and even greater than 10 microns in size. This deformation of the substrate would be in addition to the substrate shrinkage after sintering, making the tolerance of +xe2x88x920.1 micron or +xe2x88x921.0 micron difficult to achieve.
In addition, in the practice and implementation of such a packaging platform, the meaning of the dimensional tolerance of, for example, +xe2x88x921.0 micron is not made clear in the aforementioned patent. This tolerance is presumed to be an overall tolerance of the platform, not a specific tolerance quantifying the dimensional accuracy of features on said platform which may be 10-100 microns apart. This is an important point since different deformation mechanisms will play different roles in the accuracy of the alignment of two optical components depending upon the size and distance between the components. For example, grain growth after sintering may impact the achievable alignment tolerance between two optical components located approximately 2 to 10 microns apart or 10 to 100 microns apart much more than shrinkage (or bow) after sintering.
Another factor not discussed in the aforementioned patent is the impact of binders which are typically (but not always) added to ceramic powders used to make ceramic substrates. These binders are used to keep the transfer molded pre-fired ceramic substrate or part""s shape until the substrate or part has been fired or sintered. During the firing process, the binder is xe2x80x98burned offxe2x80x99 or thermally removed from the substrate or part and the formation of grain boundaries during firing play a key role in the structural stability of the substrate or part after firing.
Another factor not discussed in the aforementioned patent is the stability of the packaging platform to variations in ambient temperature. Many synthetic resins exhibit deformations in their physical geometry due to expansion and contraction of the material as the ambient temperature is changed. In the case of optical waveguide to waveguide coupling, this thermal deformation is critical to the stability of optical coupling. In fiber optic modules such as uncooled laser diodes, the change in optical coupling as a function of ambient temperature due to the change in the physical geometry of the package is typically referred to as the tracking error and can be greater than +xe2x88x921.0 dB. Thus it is desirable to form a packaging platform of a thermally stable material.
Yet another factor not discussed in the aforementioned patent is the cost effectiveness of using molded ceramics.
Several approaches have been explored to reduce the cost of packaging and assembling optical and optoelectronic modules. The work contained in U.S. Pat. No. 6,222,967 is an example of one approach. In addition to just packaging and assembly of optical and optoelectronic modules and components, much work has focused on the further integration of electronic devices with optical and optoelectronic devices to further reduce the cost of more complex optical, optoelectronic and electronic assemblies. One approach for doing this includes the use of a Silicon substrate (a so called xe2x80x98Silicon optical benchxe2x80x99) which contains features for aligning optical and optoelectronic components. The cost, complexity and limitations of both these approaches have limited the wide spread implementation of this technology.
What is required is a packaging and assembly approach which addresses the issues of optical and optoelectronic component alignment, the integration of electronic devices and the need for a simple assembly process containing not only fewer and simpler steps, but implementing fewer and less complex individual pieces.
According to this invention, substrates formed from wet or dry, hot or cold pressed ceramic powders, which powders are fired forming a finished stable substrate or platform, are used as a packaging platform and/or platform to align, position, secure and/or integrate optical, optoelectronic and/or electronic devices or components. Some optical components which can be aligned include fiber optic and integrated optic waveguides, lenses, gratings, optical filters, collimators including integrated fiber optic waveguides and lenses, metallized optical components, beam splitters, isolators, quarter- and half-wave plates, faraday rotators, polarization controlling elements, flat and curved mirrors, spatial filters, pelicals, photonic crystals, Minature Electro-Mechanical Systems (MEMS) as known in the related art, and related or similar bulk or integrated components. Some optoelectronic elements include laser diodes, photodiodes, metal-semiconductor-metal photo responsive elements, modulators, and other related components. Electrical components include any integrated circuits, transistors, resistors, capacitors, inductors, diodes, in any material, and any other related components.
A platform of the invention provides features for positioning these elements in the x, y and z directions. This platform can simplify the coupling of light from an optical or optoelectronic component to another optical or optoelectronic component or simplify the electrical coupling from an electronic or optoelectronic component to another electronic or optoelectronic component. This platform can also serve as the final packaging structure, which can be sealed or unsealed, for the integrated, aligned and/or secured optical, optoelectronic and electronic components, where said structure includes any required or desired optical, electrical and/or mechanical features. Mechanical features include, for example, holes for mounting a finished module or for guiding the attachment of, for example, a lid composed of the same or similar material.
It is another aspect of this invention to show that the use of lenses and/or collimators facilitate the use of ceramic substrates, or substrates of any material, including those mentioned in the aforementioned patent, as a packaging platform by expanding the optical beam size so that the impact of substrate deformation of any kind on the coupling of light from one component to another component can be reduced.
It is another aspect of this invention to show that the impact of grain growth can be reduced by using powders used to make ceramic substrates which contain particle sizes less than about 100 nm or less than about 500 nm. The reduction in size of the particles composing the powders used to make ceramics, including, for example, Alumina, reduces the grain growth under typical sintering conditions to  less than 1 micron.
It is another aspect of this invention to improve the alignment accuracy of components located in close proximity by using molded sintered ceramic materials made from powders which contain particle sized less than about 100 nm or less than about 500 nm.
It is another aspect of this invention to show that further improvements in the assembly process can be achieved by implementing sub mounts or secondary substrates, which are positioned and attached to the primary substrate for the purpose of aligning all types of optical and/or optoelectronic components where, for example, the optical and/or optoelectronic component needs to be positioned perpendicular to the surface of the primary substrate.
It is another aspect of this invention to improve the performance of optoelectronic and/or electronic components mounted on the described substrates by producing features which serve to isolate electrically one part of a circuit placed on the substrate from another part of a circuit placed on the substrate, or to isolate the circuit from the environment outside the packaged module or vice-versa.
It is another aspect of this invention to describe the design and assembly of fiber optic components, including new components.